File sharing systems and other publicly accessible distribution systems over the Internet are often used for distribution of copyright protected content, such distribution often comprises infringement of copyright protection laws. Such illegal or unauthorized distribution cause financial damages to the lawful content owners. It is therefore of great interest to find a method that may stop or at least reduce such acts without, at the same time, interfering with the lawful use of such systems.
Methods for copyright enforcement over digitally distributed media in file distribution and sharing systems are known. Some of the known methods are only affective for providing protection against centralized file sharing systems, where locating desired content is aided by a central server or servers providing the service. (e.g., the “Napster” file sharing service). In such a case, software on such central servers may monitor information exchange, and thereby prohibit illegal or unauthorized use. Such methods require the cooperation of the service operator or administrator. However, protection of copyrighted content delivered through decentralized distribution systems (some times known as “peer to peer” networks—e.g., “Gnutella”, “FreeNet”, “Usenet” etc'), as well as protection of copyrighted content in centralized file sharing services without the cooperation of the service operator or administrator, is much harder, and these problems are not addressed by current legal or technological methods. It is foreseeable that as the availability of disk space and bandwidth for data communication increases, illegal or unauthorized distribution of video and audio content may become prevalent unless effective counter-measures are available.